Our results indicate that a pattern of more regular GP visits rather than a sporadic pattern decreases the likelihood of all-cause mortality for older CRD patients in the highest pharmacotherapy level group and first CRD hospitalisation in patients overall.
This whole-population-based, retrospective study used linked administrative medical data for exposure and outcome ascertainment. The methodology possessed advantages in terms of minimising loss to follow-up and decreasing various forms of information bias. Furthermore, being able to collect data from a whole population meant that prima facie the study results have strong external validity. Nevertheless, a few concerns need to be addressed. Firstly, a potential reason for caution in interpreting our results was the method used to ascertain patients with CRDs. Around 70% of the patients were identified based solely on medication use without confirmation by hospital, death or MBS records. This case ascertainment strategy may have overestimated the cases of CRD in this population. However, based on data analysed by our group from 12 general practices in WA that included diagnostic information, out of 23,850 CRD prescriptions prescribed by GPs, 92% had CRD as reason for visit or prescription (unpublished data). Also, we re-performed all of our analyses separately for these 70% of patients and for the remaining 30% and found no difference between the results of analyses of the two separate groups and the aggregate analysis. Thus, by using this selection strategy we can be reasonably confident that with considerable specificity we have included all CRD cases in the older WA population who have ever seen a doctor for breathing problems. This is not surprising given that the majority of medications prescribed for CRDs do not have alternative therapeutic indications.
Secondly, immortal time bias can occur in health services research when the increased amount of health services that are needed to deal with the early symptoms of the study outcome create a false association between the services and the outcome26,27
. We endeavoured to reduce this bias by applying a 6-month ‘wash out’ period between the exposure period and the follow-up and thus excluding from the study those GP visits directly related to the early symptoms of the outcome. Applying a ‘wash out’ period of 6 months has been considered adequate to control immortal time bias in other analogous research26
. However, the possibility remains that a 6-month or even longer period may not be sufficient to remove all immortal time bias in circumstances akin to the study. Residual immortal time bias could explain the tendency for our results to show a loss of apparent advantage of high regular GP contact against mortality.
Thirdly, the PBS database was limited to dispensed medications that were subsidised by the Australian Government. However, this was unlikely to have adversely affected the study because all inhaled corticosteroid and long-acting bronchodilator medications were subsidised by the PBS, and short-acting bronchodilator medication and oral corticosteroids were consistently subsidised for pensioners29
. The latter point is especially relevant to our study as it was restricted to patients aged 65 or more years. Short-acting bronchodilator medication may have been purchased ‘over the counter’, but it was cheaper in Australia for pensioners to purchase them with a doctor’s prescription due to the PBS subsidy.
Lastly, smoking is a potential confounder in this study since it is strongly related to mortality and hospitalisation, and there is a reason to believe it is also related to the regularity of GP visits. We did not have information on smoking in our study, but our results were adjusted for a number of factors associated with smoking, such as socioeconomic status, residential remoteness, gender, indigenous status and comorbidity. Hence, although smoking status was not measured directly, its potential to cause a confounding effect was limited. Given this partial control mechanism, we do not consider that confounding by smoking is an important source of systematic error in the results.
Asthma was designated as a National Health Priority Area by the Australian health ministers in 1999. This resulted in a national Asthma Management Program commencing in 2001–2002 with an aim to improve the quality of care provided by GPs to people with moderate to severe asthma5
. Many state governments, including in Western Australia, have since then implemented strategies to encourage health professionals to improve asthma care1
. The initiative was justified given the fact that GPs play a pivotal role in the management of CRDs within the Australian health care system30
. GP visits for CRDs rarely result in referrals to secondary/tertiary care in Australia, with previous reports indicating that only 1% of patients in 2004–2007 were referred to hospitals or emergency departments1
. The importance of primary medical care in the management of CRDs has been supported by previous studies indicating that access to and patterns of GP contact can influence risk of adverse health events6,8–12
. For example, higher primary care physician density has been associated with a lower risk of potentially preventable hospital admissions12
, whilst individuals without a primary care physician8
, individuals reporting fewer physician visits9
, individuals living in primary medical care shortage areas10
, or individuals with less access to primary care11
have been found to experience more preventable hospitalisations. In addition, Tsai et al. found that patients without a primary medical care provider were more likely to visit emergency departments for COPD exacerbations6
Contained within the CRD management role of the GP are the functions of disease assessment, patient education, management of acute exacerbations and prescription of regular medications1
. Since medications are the mainstay of CRD management17–19
, the planning of therapies and education of the patient in their use represent two of the most important roles of the GP. In spite of this, CRDs have been found to be under-treated in the elderly31–34
, which has been associated with elevated risks of all-cause mortality and hospitalisation35–38
. Moreover, poor patient knowledge about asthma39,40
and the absence of an asthma management plan41,42
have been found to increase hospital emergency department visits for asthma. In light of these previous findings, the results of our study underline the importance of at least a minimum level of regular ‘maintenance’ primary medical care, as distinct from sporadic and ‘reactive’ medical care, in older patients with CRDs to manage their disease adequately and reduce the likelihood of hospitalisation and death.